APPLICATIONS

Background: Retinoblastoma-associated proteins 46 and 48 (RBAP46 and RBAP48; also known as RBBP7 and RBBP4) were first characterized in human cells as proteins that bind to the retinoblastoma (Rb) tumor suppressor protein (1). Since then, these proteins have been shown to be components of many protein complexes involved in chromatin regulation, including the chromatin assembly factor 1 (CAF-1) complex and type B histone acetyltransferase complex HAT1, both of which function in chromatin assembly during DNA replication (2,3). RBAP46 and RBAP48 are also found in the nucleosome remodeling factor complex NURF, the nucleosome remodeling and histone de-acetylation complex NuRD, and the Sin3/HDAC histone de-acetylation complex (4-7). More recently, RBAP46 and RBAP48 were identified as components of the polycomb repressor complex PRC2, which also contains EED and Ezh2 (8). RBAP46 and RBAP48 bind to the histone fold region of histone H4 and are believed to target these chromatin remodeling, histone acetylation, and histone de-acetylation complexes to their histone substrates (3).

APPLICATIONS

Background: Modulation of chromatin structure plays a critical role in the regulation of transcription and replication of the eukaryotic genome. The nucleosome, made up of four core histone proteins (H2A, H2B, H3, and H4), is the primary building block of chromatin. In addition to the growing number of post-translational histone modifications regulating chromatin structure, cells can also exchange canonical histones with variant histones that can directly or indirectly modulate chromatin structure (1). CENP-A, also known as the chromatin-associated protein CSE4 (capping-enzyme suppressor 4-p), is an essential histone H3 variant that replaces canonical histone H3 in centromeric heterochromatin (2). The greatest divergence between CENP-A and canonical histone H3 occurs in the amino-terminal tail of the protein, which binds linker DNA between nucleosomes and facilitates proper folding of centromeric heterochromatin (3). The amino-terminal tail of CENP-A is also required for recruitment of other centromeric proteins (CENP-C, hSMC1, hZW10), proper kinetochore assembly and chromosome segregation during mitosis (4). Additional sequence divergence in the histone fold domain is responsible for correct targeting of CENP-A to the centromere (5). Many of the functions of CENP-A are regulated by phosphorylation (6,7). Aurora A-dependent phosphorylation of CENP-A on Ser7 during prophase is required for proper targeting of Aurora B to the inner centromere in prometaphase, proper kinetochore/microtubule attachment and proper alignment of chromosomes during mitosis (6).

APPLICATIONS

Background: Modulation of chromatin structure plays a critical role in the regulation of transcription and replication of the eukaryotic genome. The nucleosome, made up of four core histone proteins (H2A, H2B, H3, and H4), is the primary building block of chromatin. In addition to the growing number of post-translational histone modifications regulating chromatin structure, cells can also exchange canonical histones with variant histones that can directly or indirectly modulate chromatin structure (1). CENP-A, also known as the chromatin-associated protein CSE4 (capping-enzyme suppressor 4-p), is an essential histone H3 variant that replaces canonical histone H3 in centromeric heterochromatin (2). The greatest divergence between CENP-A and canonical histone H3 occurs in the amino-terminal tail of the protein, which binds linker DNA between nucleosomes and facilitates proper folding of centromeric heterochromatin (3). The amino-terminal tail of CENP-A is also required for recruitment of other centromeric proteins (CENP-C, hSMC1, hZW10), proper kinetochore assembly and chromosome segregation during mitosis (4). Additional sequence divergence in the histone fold domain is responsible for correct targeting of CENP-A to the centromere (5). Many of the functions of CENP-A are regulated by phosphorylation (6,7). Aurora A-dependent phosphorylation of CENP-A on Ser7 during prophase is required for proper targeting of Aurora B to the inner centromere in prometaphase, proper kinetochore/microtubule attachment and proper alignment of chromosomes during mitosis (6).

APPLICATIONS

Background: Modulation of chromatin structure plays an important role in the regulation of transcription in eukaryotes. The nucleosome, made up of DNA wound around eight core histone proteins (two each of H2A, H2B, H3, and H4), is the primary building block of chromatin (1). The amino-terminal tails of core histones undergo various post-translational modifications, including acetylation, phosphorylation, methylation, and ubiquitination (2-5). These modifications occur in response to various stimuli and have a direct effect on the accessibility of chromatin to transcription factors and, therefore, gene expression (6). In most species, histone H2B is primarily acetylated at Lys5, 12, 15, and 20 (4,7). Histone H3 is primarily acetylated at Lys9, 14, 18, 23, 27, and 56. Acetylation of H3 at Lys9 appears to have a dominant role in histone deposition and chromatin assembly in some organisms (2,3). Phosphorylation at Ser10, Ser28, and Thr11 of histone H3 is tightly correlated with chromosome condensation during both mitosis and meiosis (8-10). Phosphorylation at Thr3 of histone H3 is highly conserved among many species and is catalyzed by the kinase haspin. Immunostaining with phospho-specific antibodies in mammalian cells reveals mitotic phosphorylation at Thr3 of H3 in prophase and its dephosphorylation during anaphase (11).

APPLICATIONS

Background: Modulation of chromatin structure plays an important role in the regulation of transcription in eukaryotes. The nucleosome, made up of DNA wound around eight core histone proteins (two each of H2A, H2B, H3, and H4), is the primary building block of chromatin (1). The amino-terminal tails of core histones undergo various post-translational modifications, including acetylation, phosphorylation, methylation, and ubiquitination (2-5). These modifications occur in response to various stimuli and have a direct effect on the accessibility of chromatin to transcription factors and, therefore, gene expression (6). In most species, histone H2B is primarily acetylated at Lys5, 12, 15, and 20 (4,7). Histone H3 is primarily acetylated at Lys9, 14, 18, 23, 27, and 56. Acetylation of H3 at Lys9 appears to have a dominant role in histone deposition and chromatin assembly in some organisms (2,3). Phosphorylation at Ser10, Ser28, and Thr11 of histone H3 is tightly correlated with chromosome condensation during both mitosis and meiosis (8-10). Phosphorylation at Thr3 of histone H3 is highly conserved among many species and is catalyzed by the kinase haspin. Immunostaining with phospho-specific antibodies in mammalian cells reveals mitotic phosphorylation at Thr3 of H3 in prophase and its dephosphorylation during anaphase (11).

APPLICATIONS

Background: Modulation of chromatin structure plays an important role in the regulation of transcription in eukaryotes. The nucleosome, made up of DNA wound around eight core histone proteins (two each of H2A, H2B, H3, and H4), is the primary building block of chromatin (1). The amino-terminal tails of core histones undergo various post-translational modifications, including acetylation, phosphorylation, methylation, and ubiquitination (2-5). These modifications occur in response to various stimuli and have a direct effect on the accessibility of chromatin to transcription factors and, therefore, gene expression (6). In most species, histone H2B is primarily acetylated at Lys5, 12, 15, and 20 (4,7). Histone H3 is primarily acetylated at Lys9, 14, 18, 23, 27, and 56. Acetylation of H3 at Lys9 appears to have a dominant role in histone deposition and chromatin assembly in some organisms (2,3). Phosphorylation at Ser10, Ser28, and Thr11 of histone H3 is tightly correlated with chromosome condensation during both mitosis and meiosis (8-10). Phosphorylation at Thr3 of histone H3 is highly conserved among many species and is catalyzed by the kinase haspin. Immunostaining with phospho-specific antibodies in mammalian cells reveals mitotic phosphorylation at Thr3 of H3 in prophase and its dephosphorylation during anaphase (11).

APPLICATIONS

Background: The nucleosome, made up of four core histone proteins (H2A, H2B, H3, and H4), is the primary building block of chromatin. Originally thought to function as a static scaffold for DNA packaging, histones have now been shown to be dynamic proteins, undergoing multiple types of post-translational modifications, including acetylation, phosphorylation, methylation, and ubiquitination (1). Histone methylation is a major determinant for the formation of active and inactive regions of the genome and is crucial for the proper programming of the genome during development (2,3). Arginine methylation of histones H3 (Arg2, 17, 26) and H4 (Arg3) promotes transcriptional activation and is mediated by a family of protein arginine methyltransferases (PRMTs), including the co-activators PRMT1 and CARM1 (PRMT4) (4). In contrast, a more diverse set of histone lysine methyltransferases has been identified, all but one of which contain a conserved catalytic SET domain originally identified in the Drosophila Su(var)3-9, Enhancer of zeste, and Trithorax proteins. Lysine methylation occurs primarily on histones H3 (Lys4, 9, 27, 36, 79) and H4 (Lys20) and has been implicated in both transcriptional activation and silencing (4). Methylation of these lysine residues coordinates the recruitment of chromatin modifying enzymes containing methyl-lysine binding modules such as chromodomains (HP1, PRC1), PHD fingers (BPTF, ING2), tudor domains (53BP1), and WD-40 domains (WDR5) (5-8). The discovery of histone demethylases such as PADI4, LSD1, JMJD1, JMJD2, and JHDM1 has shown that methylation is a reversible epigenetic marker (9).

APPLICATIONS

Background: The nucleosome, made up of four core histone proteins (H2A, H2B, H3, and H4), is the primary building block of chromatin. Originally thought to function as a static scaffold for DNA packaging, histones have now been shown to be dynamic proteins, undergoing multiple types of post-translational modifications, including acetylation, phosphorylation, methylation, and ubiquitination (1). Histone methylation is a major determinant for the formation of active and inactive regions of the genome and is crucial for the proper programming of the genome during development (2,3). Arginine methylation of histones H3 (Arg2, 17, 26) and H4 (Arg3) promotes transcriptional activation and is mediated by a family of protein arginine methyltransferases (PRMTs), including the co-activators PRMT1 and CARM1 (PRMT4) (4). In contrast, a more diverse set of histone lysine methyltransferases has been identified, all but one of which contain a conserved catalytic SET domain originally identified in the Drosophila Su(var)3-9, Enhancer of zeste, and Trithorax proteins. Lysine methylation occurs primarily on histones H3 (Lys4, 9, 27, 36, 79) and H4 (Lys20) and has been implicated in both transcriptional activation and silencing (4). Methylation of these lysine residues coordinates the recruitment of chromatin modifying enzymes containing methyl-lysine binding modules such as chromodomains (HP1, PRC1), PHD fingers (BPTF, ING2), tudor domains (53BP1), and WD-40 domains (WDR5) (5-8). The discovery of histone demethylases such as PADI4, LSD1, JMJD1, JMJD2, and JHDM1 has shown that methylation is a reversible epigenetic marker (9).

APPLICATIONS

Background: Modulation of chromatin structure plays a critical role in the regulation of transcription and replication of the eukaryotic genome. The nucleosome, made up of four core histone proteins (H2A, H2B, H3, and H4), is the primary building block of chromatin. In addition to the growing number of post-translational histone modifications regulating chromatin structure, cells can also exchange canonical histones with variant histones that can directly or indirectly modulate chromatin structure (1). CENP-A, also known as the chromatin-associated protein CSE4 (capping-enzyme suppressor 4-p), is an essential histone H3 variant that replaces canonical histone H3 in centromeric heterochromatin (2). The greatest divergence between CENP-A and canonical histone H3 occurs in the amino-terminal tail of the protein, which binds linker DNA between nucleosomes and facilitates proper folding of centromeric heterochromatin (3). The amino-terminal tail of CENP-A is also required for recruitment of other centromeric proteins (CENP-C, hSMC1, hZW10), proper kinetochore assembly, and chromosome segregation during mitosis (4).CENP-A is regarded as the epigenetic mark of the centromere that persists through cell generations (5). Although its presence is necessary, it is not sufficient for formation of functional kinetochores (6). CENP-T, in complex with CENP-W, has recently been shown to form a histone fold, a structure that is capable of association with DNA, and target DNA to the kinetochore (7). Kinetochore attachment is mediated by a long flexible N-terminal region that has been shown to interact with outer proteins of the kinetochore complex (reviewed in 8). Moreover, the CENP-T-W complex has also been shown to interact with the CENP-S-X dimer, to form a heterotetrameric complex that has structural and potentially functional similarity to canonical histones (8). Since CENP-S-X are conserved kinetochore localized proteins, this new complex has been suggested to be a novel centromeric histone.

APPLICATIONS

Background: Nucleophosmin (NPM; also known as B23, numatrin or NO38) is an abundant phosphoprotein primarily found in nucleoli. It has been implicated in several distinct cellular functions, including assembly and transport of ribosomes, cytoplasmic/nuclear trafficking, regulation of DNA polymerase α activity, centrosome duplication and molecular chaperoning activities (1,2). The NPM gene is also known for its fusion with the anaplastic lymphoma kinase (ALK) receptor tyrosine kinase. The NPM portion contributes to transformation by providing a dimerization domain, which results in activation of the fused kinase (3,4).

APPLICATIONS

Background: Retinoblastoma-associated proteins 46 and 48 (RBAP46 and RBAP48; also known as RBBP7 and RBBP4) were first characterized in human cells as proteins that bind to the retinoblastoma (Rb) tumor suppressor protein (1). Since then, these proteins have been shown to be components of many protein complexes involved in chromatin regulation, including the chromatin assembly factor 1 (CAF-1) complex and type B histone acetyltransferase complex HAT1, both of which function in chromatin assembly during DNA replication (2,3). RBAP46 and RBAP48 are also found in the nucleosome remodeling factor complex NURF, the nucleosome remodeling and histone de-acetylation complex NuRD, and the Sin3/HDAC histone de-acetylation complex (4-7). More recently, RBAP46 and RBAP48 were identified as components of the polycomb repressor complex PRC2, which also contains EED and Ezh2 (8). RBAP46 and RBAP48 bind to the histone fold region of histone H4 and are believed to target these chromatin remodeling, histone acetylation, and histone de-acetylation complexes to their histone substrates (3).

APPLICATIONS

Background: Retinoblastoma-associated proteins 46 and 48 (RBAP46 and RBAP48; also known as RBBP7 and RBBP4) were first characterized in human cells as proteins that bind to the retinoblastoma (Rb) tumor suppressor protein (1). Since then, these proteins have been shown to be components of many protein complexes involved in chromatin regulation, including the chromatin assembly factor 1 (CAF-1) complex and type B histone acetyltransferase complex HAT1, both of which function in chromatin assembly during DNA replication (2,3). RBAP46 and RBAP48 are also found in the nucleosome remodeling factor complex NURF, the nucleosome remodeling and histone de-acetylation complex NuRD, and the Sin3/HDAC histone de-acetylation complex (4-7). More recently, RBAP46 and RBAP48 were identified as components of the polycomb repressor complex PRC2, which also contains EED and Ezh2 (8). RBAP46 and RBAP48 bind to the histone fold region of histone H4 and are believed to target these chromatin remodeling, histone acetylation, and histone de-acetylation complexes to their histone substrates (3).

APPLICATIONS

Background: Nucleophosmin (NPM; also known as B23, numatrin or NO38) is an abundant phosphoprotein primarily found in nucleoli. It has been implicated in several distinct cellular functions, including assembly and transport of ribosomes, cytoplasmic/nuclear trafficking, regulation of DNA polymerase α activity, centrosome duplication and molecular chaperoning activities (1,2). The NPM gene is also known for its fusion with the anaplastic lymphoma kinase (ALK) receptor tyrosine kinase. The NPM portion contributes to transformation by providing a dimerization domain, which results in activation of the fused kinase (3,4).

APPLICATIONS

Background: Nucleophosmin (NPM; also known as B23, numatrin or NO38) is an abundant phosphoprotein primarily found in nucleoli. It has been implicated in several distinct cellular functions, including assembly and transport of ribosomes, cytoplasmic/nuclear trafficking, regulation of DNA polymerase α activity, centrosome duplication and molecular chaperoning activities (1,2). The NPM gene is also known for its fusion with the anaplastic lymphoma kinase (ALK) receptor tyrosine kinase. The NPM portion contributes to transformation by providing a dimerization domain, which results in activation of the fused kinase (3,4).

APPLICATIONS

Background: Reptin/RuvBL2 and Pontin/RuvBL1 are closely related members of the AAA+ (ATPase associated with diverse cellular activities) superfamily of proteins, and are putatively homologous to bacterial RuvB proteins that drive branch migration of Holliday junctions (1). Reptin and Pontin function together as essential components of chromatin remodeling and modification complexes, such as INO80, TIP60, SRCAP, and Uri1, which play key roles in regulating gene transcription (1,2). In their capacity as essential transcriptional co-regulators, Reptin and Pontin have both been implicated in oncogenic transformations, including those driven by c-Myc, β-catenin, and E1A (2-7).